The present invention relates to a shade or color determination apparatus and method for dental restorations where translucent materials are used that account for the influence of underlying tooth structure on the final shade of the dental restorations when an opaque layer of dental material is not used in the fabrication of the dental restoration.
A shade determination apparatus and method is known from U.S. Pat. No. 6,499,998 which discloses a method for specifying and determining appropriate colors for teeth and dental restorations in accordance with a set of reference templates. A shade guide such as disclosed in the '998 patent has a plurality of color groups, wherein each group is representative of a tooth with a certain brightness, saturation and/or hue and, thus, is assigned a certain shade. Each individual shade in a shade guide is termed a shade tab and is typically fabricated to resemble the shape of an upper incisor tooth with a material structure of one to as many as five or more layers of material.
A shade guide is limited in its effectiveness as a shade determination device. First, commercial shade guides have a limited number of shade tabs. Moreover, the user's ability to discern one shade from another is often compromised by the user's inability to discern small color differences due to eye strain, non-standard lighting conditions or by problems with the user's anatomy related to color discrimination.
Additional problems arise in achieving an accurate shade match using a commercial shade guide due to differences in the physical and, thus, light refractive properties of the materials used to manufacture the shade guides themselves versus the materials used to fabricate dental restorations.
While systems similar to that described in the aforementioned U.S. Pat. No 6,499,998 aim to overcome many of the limitations inherent in the use of commercial shade guides, they fail to address the influence of the color of the underlying tooth structure on the final shade of a dental restoration when translucent dental materials are used without an opaque layer to mask out the internal structure's influence.
Until recently, the use of an opaque layer in the fabrication of dental restorations was the norm. However, with the introduction and increasing use of more durable translucent dental ceramics in the fabrication of dental restorations, an opaque core material is often no longer employed. Because these ceramic restorations have no opaque core, the final color of the restoration is influenced by the color, or shade, of the prepped tooth that underlies and supports the restoration itself. However, the prior art, including U.S. Pat. No. 6,499,998, fails to take into account the significant influence of the underlying tooth structure. The present application addresses this key issue in a novel and commercially viable manner.